Oscillator tube and circuit



March 1, 1949. G. J. LEHMANN '2,462,876

OSCILLATOR TUBE AND CIRCUIT Filed oct. as, 1944 vll/lai; VII/1A f El To ac. soc/RCE /YEGHT/ v5 W/TH RESPECT T0 THE ac. .SOURCE LEAD Z3 y L /7'0 ac. 50u/zc;A g5

f@ A v INVEN TOR. GEW/4R0 J.' 'LEHMANN BY AMvB/mf Patented Mar. 1, 1949 OSCILLATOR TUBE AND CIRCUIT Gerard J. Lehmann, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application October 28, 1944, Serial No. 560,769

This invention relates to vacuum tube oscillators and their associated circuits of the type in which energy is fed back to the grid circuit through the interelectrode tube capacities,

Ordinarily in oscillators of the type referred to hereinabove, the mode of oscillation is such that the grid and plate voltages are 180 out of phase and a relatively large high frequency grid current flows. In order that such oscillators should operate efficiently, it is essential that the grid or grids be connected to the outside of the tube -by leads offering low impedance to the high frequency currents. Such low impedance leads in.- troduce serious problems in design and manufacture.

In accordance with the present invention, I have found that by producing a mode of oscillation in which the grid and plate voltages are in phase, and by proportioning the parameters of the tube and its associated circuits, as is described hereinafter, the grid or grids carry no high frequency current, and therefore the grid leads to not have to be of low impedance but merely have to be adequate to carry the D. C. potentials.

An object of the present invention is the provision of an improved vacuum tube for the purpose hereinabove described.

Another object of the present invention is the provision of an improved vacuum tube oscillator in which the grids carry no high frequency current.

A further object of the present invention is the provision of an improved vacuum tube oscillator of the type hereinabove described in which no low impedance grid leads are required and in which the leads to the grid only have to carry direct current thereto.

In accordance with my invention, I obtain the desired mode of oscillation in which the plate and grid oscillate in phase by feeding back energy through the interelectrode capacity of the tube. This energy may be fed back through any means known in the art, such as for example, by the use of a tuned plate circuit. In order to obtain this mode of oscillation, the electron transit angle should be 180 at the frequency at which said tube is designed to oscillate. Such tubes are designed to operate at a relatively narrowband of frequencies and the closer the electronic transit angle is to 180 at the frequency selected, the greater will be the efficiency obtained from this mode of oscillation. In this mode of oscillation the cathode and anode potentials are out of phase and therefore the currents 6 Claims. (Cl. 315-39) owing through the capacities anode to grid and filament to grid are in opposition and consequently the grids will draw no current if the parameters of the tube and circuit are selected such that where Vgc is the high frequency potential drop between the grid and cathode Vga is the high frequency potential drop between the grid and anode Cee is the capacity between the grid and cathode and Cga is the capacity between the grid and anode.

In accordance with this invention, where more than one grid is employed, the grid facing the anode and the grid facing the cathode are coupled by means of a relatively high capacity inside the tube so that said grids are at the same high frequency potential. The grid referred to in the above terms Cog then is the grid facing the cathode and the grid referred to in the term Cea is the grid facing the anode. Since yboth grids would be at the same high frequency potential being coupled together, it does not matter in the terms Vga and Vga which grid is considered.

Other and further objects and advantages of the present invention will become apparent and the foregoing will be best understood from the following description of an embodiment thereof, reference being had to the drawing, in which Figure 1 is a longitudinal sectional view of a vacuum tube oscillator and an associated circuit embodying my invention and Figure 2 indicates the 180 degree out of phase relation of cathode and anode voltages.

Referring to the drawing, the general structure of the tube l is in some respects similar to that of the tubes disclosed in my copending applications, Serial No. 441,105 led April 30, 1942, and patented June 25, 1946, as Patent No. 2,402,602, and Serial No. 474,085, filed January 30, 1943 and patented July 8, 1947, as Patent No. 2,423,819 and is a beam type tetrode in which the second grid focuses the beam. The insulating portions of the tube envelope consist of a portion 2, of the shape indicated, through which cathode support members 3, 4, and 5 pass and through which they are sealed. The supports 3 and 5 are also employed as current-carrying leads heating the llamentary cathode 6 which is preferably, but not necessarily, of the double spiral type. The

member 4 supports the far end of the spiral cathode, as shown.

The anode electrode may be formed from a solid block of metal 1, preferably copper. A suitable knife edge is formed on the outside ofthe block to seal it to the end of the insulating portion 2 as indicated at 8, and thus complete the tube envelope. The active portion of the block or the anode which receives the electron current from the cathode is a cylindrical surface 9 which may be formed by boring a hole in the end of the block.

Heat dissipation from the anode may be facilitated by .boring a central cavity I in that portion of the block which is exterior to the tube envelope and cutting radial grooves from said cavity I0 into the block. An air blast directed into the cavity and thence through the grooves dissipates the heat which ows into the fins existingI between the grooves.

The tube is provided with two grid electrodes I I and I2, of which grid I2 serves to focus the electron beam. Said grid electrodes II and I2 consist of a plurality of parallel bars welded at their upper ends to cone-shaped metallic members I3 and ill, respectively, members I3 and I4 being supported by any suitable means such as glass beads I5 from the top of insulating portion 2. Conical members I3 and I4 'are arranged close to each other and have a relatively large surface area so that a high capacity is formed therebetween connecting the two grids. Cones I 3 and I4 and consequently grids Il and I2 are connected externally by means of leads I6 and I'I passing through and sealed in the insulating portion 2 of the envelope and connected inside the envelope to cones I3 and Id. In accordance with my invention, these leads do not have to be low impedance leads but preferably are leads sui'ci'ent to carry the D. C. potentials which are applied to the respective grids and are of high impedance at the frequencies at which said tube is designed to oscillate. I

The oscillatory circuit associated with said tube is arranged as follows:

An inner conductive cylinder I8 is connected to cathode support member 4 and consequently to the cathode, cathode support members 3 and 5 passing through the interior of said cylinder. Tube i and cylinder I3 are mounted within a large outer conductive cylinder I9. A cylinder 20, similar to I8, is connected to the portion of the anode block exterior to the tube and is likewise mounted within cylinder I9. The electrical length from the end of cylinder 20 to the opposite end oi anode 9 is preferably substantially half a wavelength at the operating frequency of said device. A shorting plunger 2| is arranged between cylinder i3 and cylinder I9 and is ladapted to be moved to tune the anode to cathode circuit. rihe cylinders may be considered as forming a resonant cavity chamber tuned by shorting plunger 2 I.

The high frequency oscillatory energy of this system may be derived as output in various ways known in the art. For this purpose, in the embodiment illustrated, an output coupling loop 22 is inserted through an opening in cylinder I9.

rihe direct current connections to the grids may be made by passing leads I6 and I1 through suitable openings in cylinder I9 and connecting them to D, C. sources. Likewise the D. C.' potential for the anode may be supplied by' a line 23 passing through a suitable opening in cylinder I9 and connected to the portion of the anode block exterior to said envelope, the other end of said line 23 being connected to apositive source of D. C. anode potential.

It will be seen that in the system shown the feedback is made through the interelectrode capacities and that this is accomplished by tuning the anode-cathode circuit. Grids Il and I2 are maintained at the same high frequency potential because of the relatively high capacity between members I3 and I4. In order to obtain the mode of oscillation hereinbefore mentioned, that is, the potentials of the grids and anode being in phase, the electronic transit angle is made substantially equal to or stated in another way the electron transit time is equal to half the period of a complete oscillation at the operating frequency of the system. This is accomplished, as is known in the art, by suitably spacing the yanode and cathode and applying proper potentials therebetween. Moreover in order to maintain the grids at the null potential point relative to the instantaneous anode and cathode potentials so that the grids carry no high frequency currents, the parameters of the circuit are selected such that the product of the instantaneous alternating current voltage and the capacity between cathode 6 and grid i I is equal to the product of the instantaneous alternating current voltage and capacity between grid IZ and anode 9. By adjusting the D. C. potentials applied to the anode, grids, and cathode in relation to the interelectrode capacities, this condition is readily fullled,

While I have described the tube as being a tetrode, my invention may also be employed with triodes or other multi-element tubes.A Furthermore, while I have shown one type of ycircuit associated with said tube, it is obvious that various other forms of circuits depending for their oscillation on the feedback of energy through their interelectrode tube capacities may be employed.

Accordingly, while I have described above the principles of my invention in connection with specic apparatus, it is to be clearly understood that this description is made only Iby way of eX- ample and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claims.

I claim:

l. In a vacuum tube oscillator, the combination according to claim 4 wherein the means for feeding energy back to the cathode includes a tuned anode-cathode circuit. i

2. In a vacuum tube oscillator, the combination according to claim 4 wherein the means for feeding back energy to the cathode includes a tuned cavity resonator interconnecting the anode and cathode. l

3. In a vacuum tube oscillator, the combination according to claim 4 wherein the means for feeding back energy is comprised of a conductive cylinder connected to the cathode, a conductive cylinder connected to the anode, a larger cylinder surrounding said cathode and anode cylinders and capacitively coupled thereto, and movable shorting means connected between said larger cylinder and one of the other cylinders.

4. A vacuum tube oscillator comprising a'vacuurn tube having a `cathode rst and second grids, and an anode mounted in the order named, means arranged between said grids for provi-ding large capacitance therebetween at an operating lfrequency to maintain said grids at the same high frequency potential, means coupled between said anode and cathode and including the interelectrode capacities for providing a feedback path from said anode to said cathode having a 180 phase shift at the operating-frequency, the di"-` men-sionsof said-tube being such that the' electron" VgcX Cgc=VgaXCga where Vga is the alternating current Voltage between grid and cathode, Vga is the alternating current voltage between grid and anode, Cgc is the capacity between grid and cathode, and Cg is the capacity between grid and anode.

6. A vacuum tube oscillator according to claim 4 in which said means for providing large capacitance comprises concentric cones, one connected to each of said grids and mounted closely adjacent one another.

GERARD J. LEHMANN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES 'PATENTS Number Name Date 2,128,232 Dallenbach Aug. 30, 1938 2,207,846 Wolff .July 16, 1940 2,244,747 Varian et al June 10, 1941 2,272,211 Kohler Feb. 10, 1942 2,287,845 Varian et a1 June 30, 1942 2,353,742 McArthur July 18, 1944 

